389  
FXUS10 KWNH 121829  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
229 PM EDT THU OCT 12 2017  
 
VALID OCT 12/1200 UTC THRU OCT 16/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
FADING SYSTEM MOVING OUT OF MID-ATLANTIC TODAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z CMC CONTINUES TO BE QUICKER TO SHEAR INTO THE MEAN FLOW AS  
THE SYSTEM SLIDES THROUGH THE MID-ATLANTIC AND NEAR COASTAL ZONES  
THROUGH REMAINDER OF TODAY. THIS IS OPPOSED BY A MORE AGREEABLE  
SOLUTION OF THE REMAINING DETERMINISTIC GUIDANCE AND ENSEMBLE  
MEMBERS OF THE GEFS/ECENS. AS SUCH A NON-CMC BLEND REMAINS  
PREFERENCE AT ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: NO SIGNIFICANT CHANGE...THE CMC REMAINS SLIGHTLY  
WEAKER/FASTER.  
 
FRONT MOVING INTO THE GREAT LAKES/NORTHEAST FRIDAY/SATURDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
SOLID MODEL AGREEMENT IN TIMING/DEPTH/ORIENTATION OF THE FRONTAL  
ZONE CROSSING THE GREAT LAKES LATE FRIDAY AND SLIDING INTO THE  
NORTHEAST SAT...LINGERING BACK INTO THE CENTRAL PLAINS/WESTERN  
MIDWEST. AS SUCH A GENERAL MODEL BLEND IS PREFERENCE AT HIGHEST  
LEVELS OF CONFIDENCE.  
 
19Z UPDATE: NO SIGNIFICANT CHANGES NOTED WITH THE 12Z  
CMC/UKMET/ECWMF OR GEFS SOLUTIONS TO CHANGE INITIAL PREFERENCE.  
 
TROPICAL WAVE/UPPER LOW MOVING THROUGH THE FL STRAITS FRIDAY  
LINGERING ENERGY NORTH OF THE BAHAMAS THROUGH THE WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 00Z CMC REMOVED THE STRONGER LAGGING SHORTWAVE AT THE APEX OF  
THE POSITIVELY TITLED INVERTED TROPICAL TROF OFF NEAR THE BAHAMAS  
ON FRIDAY...AND IS NOW SLIGHTLY FASTER AND FURTHER SOUTHEAST WITH  
THE SURFACE REFLECTION THAN OTHER DETERMINISTIC GUIDANCE. MOST  
GUIDANCE IS FAIRLY CONSISTENT IN DEAMPLIFYING THE TROF THROUGH  
FRI/SAT MOVING OUT OF THE FL STRAITS TOWARD THE YUCATAN. HOWEVER  
THE NCEP GUIDANCE AND IN PARTICULAR THE 12Z NAM RETAINS SOME  
STRONGER MID-LEVEL SHORTWAVE ENERGY AT THE APEX OF THE TROF NORTH  
OF THE BAHAMAS THROUGH THE WEEKEND. WHILE THE GFS AND EVENTUALLY  
THE 00Z ECMWF/CMC RECONSOLIDATE/ADVECT ENERGY WESTWARD TOWARD THE  
BAHAMAS BY LATE SUN...THE NAM APPEARS A CLEAR OUTLIER TO THE  
OVERALL EVOLUTION. ENOUGH TO SUGGEST A NON-NAM BLEND AT SLIGHTLY  
ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: THE 12Z CMC/UKMET CONTINUE TO BE QUICKER DEAMPLIFYING  
AND SHIFTING SW TOWARD THE YUCATAN WHILE THE 12Z ECMWF MATCHES  
BETTER WITH THE GFS...THOUGH THE DIFFERENCES BETWEEN THOSE ARE NOT  
AS SUBSTANTIAL AS THE 12Z NAM...SO WILL CONTINUE A NON-NAM  
PREFERENCE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
SYSTEM MOVING FROM THE NORTHWEST FRI/SAT INTO THE GREAT LAKES SUN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
LEAD SHORTWAVE/HEIGHT FALLS ARE DETECTED IN GOES-W WV APPROACHING  
PACIFIC NW WITH ELONGATED EXTENSION OF THE VORTICITY STRIP ALONG  
THE BC COAST INTO AK. THIS LEAD WAVE IS EXPECTED TO REINFORCE THE  
WESTERN TROF AS THE PRIOR WAVE LIFTS INTO CANADA (SEE 'FRONT' 2  
SECTIONS ABOVE)...WHILE THE SECOND UPSTREAM PORTION CONSOLIDATES  
AND ROUNDS OUT THE BASE OF THE TROF. THE TIMING AND STRENGTH  
GIVEN TO EACH PORTION LEAD TO FAIRLY LARGE DOWNSTREAM MODEL SPREAD  
AS THE TROF EVOLVES/TRANSLATES EASTWARD. RUN TO RUN ENSEMBLE  
TRENDS DEPICT A CLEAR DEEPER LEAD WAVE TRANSLATING ACROSS THE  
DAKOTAS MIDDAY TO LATE SAT; HOWEVER SPACING BETWEEN THE UPSTREAM  
WAVE ALSO FURTHER EXPAND THE MODEL SPREAD... WITH SHORTER  
DISTANCES/ALMOST CONSOLIDATION PRESENTED BY THE RECENT RUNS OF THE  
NAM AND GFS...BOTH PRESENTING CLOSED 7H TO 5H CIRCULATIONS A BIT  
EARLIER THAN ECMWF. THE CMC/UKMET BOTH ARE VERY FLAT OVERALL  
HAVING GREATER SPACING LINGERING THE SHORTWAVE UPSTREAM ACROSS THE  
ROCKIES A BIT LONGER...EVENTUALLY BECOMING WELL OUT OF PHASE WITH  
THE ENSEMBLES AND TREND INTO SUN. THE 12Z ECMWF SUPPORTED BY A  
MAJORITY OF ECENS MEMBERS IS A BLEND OF THE WELL WOUND UP GFS/NAM  
SOLUTIONS AND THE UKMET/CMC. THE 12Z NAM SIGNIFICANTLY SHIFTED  
FASTER WITH THE TROF AND DEEPENING SFC CYCLONE ACROSS THE GREAT  
LAKES BY SUNDAY BUT REMAINS WELL SLOWER THAN THE ENSEMBLE MEANS  
AND EVEN THE TYPICALLY SLOWER CMC. THE 12Z GFS SHIFTED SOUTHWARD  
SLOWED EVER SO SLIGHTLY AND IS LESS CONCENTRIC (ELONGATES 5H INTO  
CENTRAL PLAINS/LOWER OH VALLEY) AND GENERALLY CONVERGE WITH  
ECMWF/GEFS SOLUTIONS BY 00Z MON. FAIRLY TIGHT 00Z/06Z GEFS MEMBERS  
WITHIN THE SFC CLUSTERING IS FAIRLY IMPRESSIVE GIVEN THE OVERALL  
LARGE SPREAD IN THE REMAINING GUIDANCE/ECENS MEMBERS BUT SUPPORTS  
THE OVERALL TIMING IN THE ECENS MEAN...ENOUGH TO PROVIDE SOME WEAK  
CONFIDENCE TOWARD THIS COMBINATION AS PREFERENCE. THE 12Z GFS AND  
00Z ECMWF SEEM TO BE A SOLID REPRESENTATION OF THE  
ENSEMBLES/TRENDS TO MAKE IT WPC PREFERENCE...CONFIDENCE IS AVERAGE  
IN THIS SOLUTION.  
 
19Z UPDATE: LARGE CHANGES FOR THE 12Z CMC AND UKMET BOTH TRENDED A  
BIT DEEPER FURTHER NORTH AS THE LEAD SHORTWAVE ROTATES THROUGH THE  
BASE OF THE TROF AND EMERGES INTO THE NORTHERN PLAINS...WITH THE  
TRAILING POSITIVE TILT TROF MOVING THROUGH INTO THE CENTRAL PLAINS  
BY SUN. AS SUCH THE OVERALL MASS FIELDS HAVE TRENDED MUCH CLOSER  
TO THE INITIAL PREFERENCE. HOWEVER...THE 12Z UKMET SHOWS SOME OF  
ITS FAST BIAS WHILE THE CMC IS IN A MORE TYPICAL SLOWER POSITION  
RELATIVELY WHICH KEEPS IT A SOUTHERN MEMBER OF THE SUITE WITH  
RESPECT TO THE SURFACE LOW TRACK. THE 12Z ECMWF SHOWS SOME GOOD  
CONSISTENCY WITH THE 00Z RUN BUT HAS SLOWED A BIT TO BETTER MATCH  
THE 12Z GFS. TO ENCOMPASS MORE UNCERTAINTY AND SPREAD A NON-NAM  
SOLUTION COULD BE PREFERRED THOUGH WITH TIGHTER OVERALL AGREEMENT  
WILL CONTINUE TO SUGGEST A 12Z GFS/ECMWF BLEND AND IN DOING SO  
INCREASE CONFIDENCE TO SLIGHTLY ABOVE AVERAGE.  
 
RAPID ESE MOVING KICKER SHORTWAVE ACROSS S CANADA INTO US NORTHERN  
TIER BY SUN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/UKMET/ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
AS NORMAL WITH KICKER WAVES...IF THE TIMING/ORIENTATION OF THE  
MAIN DOWNSTREAM WAVE IS OFF...THE KICKER WILL LIKELY BE OFF AS  
WELL; AND AS SUCH A SIMILAR TIMING AND SHAPE/EVOLUTION OF THE  
KICKER WITH THE 12Z GFS AND 00Z ECMWF LOOK QUITE REASONABLE GIVEN  
STRENGTH/SPEED OF THE AMBIENT FLOW. THE 00Z CMC/UKMET WHILE NOT  
IDEALLY ORIENTATED/SHAPED SHOW CONFIDENCE TOWARD THE TIMING OF THE  
SHORTWAVE PRESENTED BY THE GFS/ECMWF EVEN WITH LESS DESIRABLE  
FEEDBACK FROM THE UNFAVORABLE DOWNSTREAM EVOLUTION. SIMILARLY  
THE 12Z NAM SEEMS WELL TIMED BUT GIVEN THE VERY SLOW/AMPLIFIED  
NATURE DOWNSTREAM ON SUNDAY...THIS WAVE IS ABLE TO DIGS  
SOUTH/AMPLIFY IN THE GREATER LARGER SCALE CYCLONIC FLOW MAKING IT  
THE MOST ON THE FRINGE OF GUIDANCE. STILL THE OVERALL SUITE  
PROVIDES AVERAGE TO SLIGHTLY ABOVE AVERAGE CONFIDENCE IN A 12Z  
GFS/00Z ECMWF BLEND FOR PREFERENCE.  
 
19Z UPDATE: THE 12Z ECMWF TRENDED A BIT FLATTER/WEAKER OVERALL  
WITH THE SHORTWAVE AND AS SUCH THE TRACK IS FURTHER NORTH THAN THE  
00Z RUN OR THE 12Z GFS/INITIAL PREFERENCE. THE 12Z CMC LIKE THE  
NAM IS SLOWER AND MORE AMPLIFIED (LIKELY DUE TO THE RELATIVELY  
SLOWER DOWNSTREAM WAVE). THE 12Z UKMET WHILE FASTER THAN THE  
OTHER GUIDANCE EVOLVES IN A SIMILAR MANNER/DEPTH TO THE  
ECMWF/GFS...SPLITTING THE DIFFERENCES IN LATITUDE OF THE  
GFS/ECMWF. ALL CONSIDERED A BLEND OF THE 12Z ECMWF/UKMET/GFS  
SEEMS PRUDENT...THOUGH WITH INCREASED SPREAD CONFIDENCE IS LOWERED  
TO AVERAGE IN THIS BLEND.  
 
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